This invention relates to reusable heat sources, and to methods for their use, which devices contain a supercooled material, either as a melt or in a solution, which, when crystallized, liberates heat.
Many types of heat devices are known which employ a supercooled melt or aqueous salt solution. These heat devices are stored with the heat source maintained as a supercooled melt or solution. When needed, the devices can be activated by crystallization of the melt or the salt in solution with the resulting release of heat.
An example of such a heat device and a method for its use is disclosed in U.S. Pat. No. 4,077,390. Therein a heat pack containing a supercooled aqueous sodium acetate solution is used as the heat source. Activation, i.e. crystallization, is accomplished using a flexible metal strip contained in the heat pack. Crystallization of the sodium acetate results in the liberation of heat.